(CNN) -- Three ballistic missile crew members have been punished for sleeping during a sensitive task, the Air Force reported Thursday.

Two first lieutenants and a captain fell asleep on July 12 while in control of a classified electronic part that contained old launch codes for intercontinental nuclear missiles. It happened during the changing out of electronic parts used to communicate with Minot Air Force Base in North Dakota.

Maj. Laurie A. Arellano, an Air Force spokeswoman, confirmed to CNN they have been "decertified from missile operations," been given written reprimands and will forgo part of their pay for two months. This comes under an Article 15 procedure that allows for discipline without court action.

She said two squadron commanders are among six other officers who were sanctioned for their roles in the incident, and disciplinary letters are in their files.

Two officers are under investigation for lying about destroying classified missile components, and another for alleged sexual misconduct, the military reported.

A crew member formerly from the 91st Missile Wing told the military last May that he and another officer formerly assigned to the wing didn't tell the truth about destroying classified launch devices in July 2005, Arellano said.

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Such devices are approximately the size of a bandage and are used on equipment inside the launch control center to detect any equipment tampering, the Air Force says.

Arellano said they were expected to destroy the items and they signed documents that said the material was destroyed.

But the one officer who came forward said each man took one of the items home, Arellano said. That crew member who notified the Air Force turned over his device, but it is not known what happened to the other device, Arellano said.

The two have been reassigned to other capacities while the investigation continues. Arellano said there is no security risk since the material that was expected to be destroyed had been overridden.

Another incident involved alleged sexual contact at Malmstrom Air Force Base in Montana. Arellano said the Air Force was told in March that a male crew member sexually assaulted a woman in December while they were on duty in a launch control area.

The man also has been reassigned during the probe and Arellano said she didn't know the duty status of the woman.

"There is no more important mission anywhere than maintaining the readiness, safety and security of our nuclear weapons. We are fully committed to demonstrating to the American people we deserve their trust to do that mission." said Gen. C. Robert Kehler, head of the Air Force Space Command, quoted in an Air Force news release.

"Each violation of our very exacting standards is fully investigated, and every person at all levels is held fully accountable for their actions."

There have been a string of Air Force mishaps and problems relating to weapons.

A truck carrying an unarmed missile booster tipped over in North Dakota in July. The vehicle, which was carrying a Minuteman III rocket booster, tipped on its side on a gravel road about 70 miles southwest of Minot Air Force Base. The crew received only minor injuries.

Last August, a B-52 bomber flew from Minot to Louisiana with the crew unaware that six nuclear-tipped missiles were onboard, and a shipment of components that arm and fuse nuclear warheads was accidentally sent to Taiwan in 2006.

An investigation prompted by those incidents led to the firing of Air Force Secretary Michael W. Wynne and Chief of Staff Gen. T. Michael Moseley.